LM4990
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LM4990
SNAS184E – DECEMBER 2002 – REVISED MAY 2013
2 Watt Audio Power Amplifier with Selectable
Shutdown Logic Level
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FEATURES
DESCRIPTION
•
The LM4990 is an audio power amplifier primarily
designed for demanding applications in mobile
phones and other portable communication device
applications. It is capable of delivering 1.25 watts of
continuous average power to an 8Ω BTL load and 2
watts of continuous average power (NGZ and DGQ
only) to a 4Ω BTL load with less than 1% distortion
(THD+N+N) from a 5VDC power supply.
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2
•
•
•
•
•
•
•
Available in Space-Saving Packages: WSON,
Exposed-DAP MSOP-PowerPAD, VSSOP, and
DSBGA
Ultra Low Current Shutdown Mode
Improved Click and Pop Circuitry Eliminates
Noise During Turn-On and Turn-Off
Transitions
2.2 - 5.5V Operation
No Output Coupling Capacitors, Snubber
Networks or Bootstrap Capacitors Required
Unity-Gain Stable
External Gain Configuration Capability
User Selectable Shutdown High or Low Logic
Level
APPLICATIONS
•
•
•
Mobile Phones
PDAs
Portable Electronic Devices
KEY SPECIFICATIONS
•
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Improved PSRR at 217Hz & 1KHz: 62dB
Power Output at 5.0V, 1% THD+N,
– 4Ω (NGZ and DGQ only): 2W (Typ)
Power Output at 5.0V, 1% THD+N, 8Ω: 1.25W
(Typ)
Power Output at 3.0V, 1% THD+N, 4Ω: 600mW
(Typ)
Power Output at 3.0V, 1% THD+N, 8Ω: 425mW
(Typ)
Shutdown Current: 0.1µA (Typ)
Boomer audio power amplifiers were designed
specifically to provide high quality output power with a
minimal amount of external components. The
LM4990 does not require output coupling capacitors
or bootstrap capacitors, and therefore is ideally suited
for mobile phone and other low voltage applications
where minimal power consumption is a primary
requirement.
The LM4990 features a low-power consumption
shutdown mode. To facilitate this, Shutdown may be
enabled by either logic high or low depending on
mode selection. Driving the shutdown mode pin either
high or low enables the shutdown pin to be driven in
a likewise manner to enable shutdown.
The LM4990 contains advanced pop & click circuitry
which eliminates noise which would otherwise occur
during turn-on and turn-off transitions.
The LM4990 is unity-gain stable and can be
configured by external gain-setting resistors.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2002–2013, Texas Instruments Incorporated
LM4990
SNAS184E – DECEMBER 2002 – REVISED MAY 2013
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Connection Diagram
Figure 1. VSSOP Package – Top View
See Package Number DGK
Figure 2. WSON Package – Top View
See Package Number NGZ0010B
Figure 3. Exposed-DAP MSOP-PowerPAD
Package – Top View
See Package Number DGQ
Figure 4. 9-Bump DSBGA (Top View)
See Package Number YZR0009
Package
Shutdown Mode
Typical Power Output at 5V, 1% THD+N
2
NGZ
DGQ
DGK
YZR
Selectable
Selectable
Low
Low
2W (RL = 4Ω)
2W (RL = 4Ω)
1.25W (RL = 8Ω)
1.25W (RL = 8Ω)
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Typical Application
Note: DGK and YZR packaged devices are active low only; Shutdown Mode pin is internally tied to GND.
Figure 5. Typical Audio Amplifier Application Circuit (NGZ and DGQ)
Figure 6. Typical Audio Amplifier Application Circuit (YZR and DGK)
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings (1) (2)
Supply Voltage (3)
6.0V
−65°C to +150°C
Storage Temperature
−0.3V to VDD +0.3V
Input Voltage
Power Dissipation
(4) (5)
Internally Limited
ESD Susceptibility (6)
2000V
ESD Susceptibility (7)
200V
Junction Temperature
150°C
θJC (VSSOP)
56°C/W
θJA (VSSOP)
Thermal Resistance
θJA (9 Bump DSBGA)
190°C/W
(8)
180°C/W
θJA (WSON)
63°C/W (9)
θJC (WSON)
12°C/W (9)
Soldering Information: See the AN-1187 Application Report
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional but specific performance is not ensured. Electrical Characteristics state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good
indication of device performance.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
If the product is in Shutdown mode and VDD exceeds 6V (to a max of 8V VDD), then most of the excess current will flow through the
ESD protection circuits. If the source impedance limits the current to a max of 10mA, then the device will be protected. If the device is
enabled when VDD is greater than 5.5V and less than 6.5V, no damage will occur, although operation life will be reduced. Operation
above 6.5V with no current limit will result in permanent damage.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature
TA. The maximum allowable power dissipation is PDMAX = (TJMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever
is lower. For the LM4990, see power derating curves for additional information.
Maximum power dissipation in the device (PDMAX) occurs at an output power level significantly below full output power. PDMAX can be
calculated using Equation 1 shown in the Application Information section. It may also be obtained from the power dissipation graphs.
Human body model, 100pF discharged through a 1.5kΩ resistor.
Machine Model, 220pF – 240pF discharged through all pins.
All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. All bumps must be
connected to achieve specified thermal resistance.
The Exposed-DAP of the NGZ0010B package should be electrically connected to GND or an electrically isolated copper area. the
LM4990LD demo board has the Exposed-DAP connected to GND with a PCB area of 86.7mils x 585mils (2.02mm x 14.86mm) on the
copper top layer and 550mils x 710mils (13.97mm x 18.03mm) on the copper bottom layer.
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
4
−40°C ≤ TA ≤ 85°C
2.2V ≤ VDD ≤ 5.5V
Supply Voltage
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Electrical Characteristics VDD = 5V (1) (2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4990
Typical (3)
Limit (4) (5)
Units
(Limits)
VIN = 0V, Io = 0A, No Load
3
7
mA (max)
VIN = 0V, Io = 0A, 8Ω Load
4
10
mA (max)
VSD = VSD Mode (6)
0.1
2.0
µA (max)
Shutdown Voltage Input High
VSD MODE = VDD
1.5
V
Shutdown Voltage Input Low
VSD MODE = VDD
1.3
V
VSDIH
Shutdown Voltage Input High
VSD MODE = GND
1.5
V
VSDIL
Shutdown Voltage Input Low
VSD MODE = GND
1.3
VOS
Output Offset Voltage
IDD
Quiescent Power Supply Current
ISD
Shutdown Current
VSDIH
VSDIL
ROUT
7
Resistor Output to GND (7)
8.5
kΩ (min)
0.9
W (min)
THD+N = 1% (max); f = 1kHz
2
W
100
ms
0.2
%
THD+N
+N
Total Harmonic Distortion+Noise
Po = 0.5Wrms; f = 1kHz
PSRR
Power Supply Rejection Ratio
Vripple = 200mV sine p-p
Input terminated with 10Ω
(9)
7.0
(4Ω) (8) (9)
Wake-up time
(8)
kΩ (max)
1.25
TWU
(7)
9.7
THD+N = 1% (max); f = 1kHz
Output Power
(2)
(3)
(4)
(5)
(6)
mV (max)
(8Ω)
Po
(1)
V
50
60 (f = 217Hz)
64 (f = 1kHz)
55
dB (min)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional but specific performance is not ensured. Electrical Characteristics state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good
indication of device performance.
All voltages are measured with respect to the ground pin, unless otherwise specified.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
For DSBGA only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a
maximum of 2µA.
RROUT is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the
two 20kΩ resistors.
The Exposed-DAP of the NGZ0010B package should be electrically connected to GND or an electrically isolated copper area. the
LM4990LD demo board has the Exposed-DAP connected to GND with a PCB area of 86.7mils x 585mils (2.02mm x 14.86mm) on the
copper top layer and 550mils x 710mils (13.97mm x 18.03mm) on the copper bottom layer.
The thermal performance of the WSON and exposed-DAP MSOP-PowerPAD packages when used with the exposed-DAP connected to
a thermal plane is sufficient for driving 4Ω loads. The VSSOP and DSBGA packages do not have the thermal performance necessary
for driving 4Ω loads with a 5V supply and is not recommended for this application.
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Electrical Characteristics VDD = 3V (1) (2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4990
Typical (3)
Limit (4) (5)
Units
(Limits)
VIN = 0V, Io = 0A, No Load
2
7
mA (max)
VIN = 0V, Io = 0A, 8Ω Load
3
9
mA (max)
VSD = VSD Mode (6)
0.1
2.0
µA (max)
Shutdown Voltage Input High
VSD MODE = VDD
1.1
V
Shutdown Voltage Input Low
VSD MODE = VDD
0.9
V
VSDIH
Shutdown Voltage Input High
VSD MODE = GND
1.3
V
VSDIL
Shutdown Voltage Input Low
VSD MODE = GND
1.0
VOS
Output Offset Voltage
IDD
Quiescent Power Supply Current
ISD
Shutdown Current
VSDIH
VSDIL
ROUT
7
Resistor Output to GND (7)
8.5
7.0
kΩ (min)
mW
(4Ω)
THD+N = 1% (max); f = 1kHz
600
mW
75
ms
0.1
%
Wake-up time
THD+N
+N
Total Harmonic Distortion+Noise
Po = 0.25Wrms; f = 1kHz
PSRR
Power Supply Rejection Ratio
Vripple = 200mV sine p-p
Input terminated with 10Ω
6
kΩ (max)
425
TWU
(7)
9.7
THD+N = 1% (max); f = 1kHz
Output Power
(2)
(3)
(4)
(5)
(6)
mV (max)
(8Ω)
Po
(1)
V
50
62 (f = 217Hz)
68 (f = 1kHz)
55
dB (min)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional but specific performance is not ensured. Electrical Characteristics state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good
indication of device performance.
All voltages are measured with respect to the ground pin, unless otherwise specified.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
For DSBGA only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a
maximum of 2µA.
RROUT is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the
two 20kΩ resistors.
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Electrical Characteristics VDD = 2.6V (1) (2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LM4990
Typical (3)
Limit (4) (5)
Units
(Limits)
VIN = 0V, Io = 0A, No Load
2.0
mA
VIN = 0V, Io = 0A, 8Ω Load
3.0
mA
Shutdown Current
VSD = VSD Mode (6)
0.1
µA
VSDIH
Shutdown Voltage Input High
VSD MODE = VDD
1.0
V
VSDIL
Shutdown Voltage Input Low
VSD MODE = VDD
0.9
V
VSDIH
Shutdown Voltage Input High
VSD MODE = GND
1.2
V
VSDIL
Shutdown Voltage Input Low
VSD MODE = GND
1.0
VOS
Output Offset Voltage
IDD
Quiescent Power Supply Current
ISD
ROUT
Po
5
Resistor Output to GND (7)
Output Power
8.5
( 8Ω )
THD+N = 1% (max); f = 1kHz
300
( 4Ω )
THD+N = 1% (max); f = 1kHz
400
TWU
Wake-up time
THD+N
+N
Total Harmonic Distortion+Noise
Po = 0.15Wrms; f = 1kHz
PSRR
Power Supply Rejection Ratio
Vripple = 200mV sine p-p
Input terminated with 10Ω
(1)
(2)
(3)
(4)
(5)
(6)
(7)
V
50
mV (max)
9.7
kΩ (max)
7.0
kΩ (min)
mW
70
ms
0.1
%
51 (f = 217Hz)
51 (f = 1kHz)
dB
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional but specific performance is not ensured. Electrical Characteristics state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good
indication of device performance.
All voltages are measured with respect to the ground pin, unless otherwise specified.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
For DSBGA only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a
maximum of 2µA.
RROUT is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the
two 20kΩ resistors.
External Components Description
See (Figure 5)
Components
Functional Description
1.
Ri
Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a high pass
filter with Ci at fC= 1/(2π RiCi).
2.
Ci
Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a highpass filter with
Ri at fc = 1/(2π RiCi). Refer to the section, PROPER SELECTION OF EXTERNAL COMPONENTS, for an explanation
of how to determine the value of Ci.
3.
Rf
Feedback resistance which sets the closed-loop gain in conjunction with Ri.
4.
CS
Supply bypass capacitor which provides power supply filtering. Refer to the POWER SUPPLY BYPASSING section for
information concerning proper placement and selection of the supply bypass capacitor.
5.
CB
Bypass pin capacitor which provides half-supply filtering. Refer to the section, PROPER SELECTION OF EXTERNAL
COMPONENTS, for information concerning proper placement and selection of CB.
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Typical Performance Characteristics
NGZ and DGQ Specific Characteristics
THD+N+N vs Frequency
VDD = 5V, RL = 4Ω, and PO = 1W
THD+N+N vs Output Power
VDD = 5V, RL = 4Ω, and f = 1 kHz
1
1
THD+N (%)
10
THD+N (%)
10
0.1
0.01
20
8
0.1
100
1k
10k 20k
0.01
10m
100m
FREQUENCY (Hz)
OUTPUT POWER (W)
Figure 7.
Figure 8.
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Typical Performance Characteristics
THD+N+N vs Frequency
VDD = 5V, RL = 8Ω, and PO = 500mW
THD+N+N vs Frequency
VDD = 3V, RL = 4Ω, and PO = 500mW
1
1
THD+N (%)
10
THD+N (%)
10
0.1
0.1
0.01
20
100
1k
0.01
20
10k 20k
100
1k
10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 9.
Figure 10.
THD+N+N vs Frequency
VDD = 3V, RL = 8Ω, and PO = 250mW
THD+N+N vs Frequency
VDD = 2.6V, RL = 4Ω, and PO = 150mW
1
1
THD+N (%)
10
THD+N (%)
10
0.1
0.1
0.01
20
100
1k
0.01
20
10k 20k
100
1k
10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 11.
Figure 12.
THD+N+N vs Output Power
VDD = 2.6V, RL = 8Ω, and PO = 150mW
THD+N+N vs Output Power
VDD = 5V, RL = 8Ω, and f = 1kHz
1
1
THD+N (%)
10
THD+N (%)
10
0.1
0.01
20
0.1
100
1k
10k 20k
0.01
10m
100m
FREQUENCY (Hz)
OUTPUT POWER (W)
Figure 13.
Figure 14.
1
3
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Typical Performance Characteristics (continued)
THD+N+N vs Output Power
VDD = 3V, RL = 4Ω, and f = 1kHz
THD+N+N vs Output Power
VDD = 3V, RL = 8Ω, and f = 1kHz
1
1
THD+N (%)
10
THD+N (%)
10
0.1
0.1
0.01
10m
100m
0.01
10m
1
1
OUTPUT POWER (W)
Figure 15.
Figure 16.
THD+N+N vs Output Power
VDD = 2.6V, RL = 4Ω, and f = 1kHz
THD+N+N vs Output Power
VDD = 2.6V, RL = 8Ω, and f = 1kHz
1
1
THD+N (%)
10
THD+N (%)
10
0.1
0.1
0.01
10m
100m
0.01
10m
1
100m
500m
OUTPUT POWER (W)
Figure 17.
Figure 18.
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 5V, RL = 8Ω, input 10Ω terminated
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 5V, RL = 8Ω, input floating
0
0
-10
-10
-20
-20
-30
-30
PSRR LEVEL (dB)
PSRR LEVEL (dB)
OUTPUT POWER (W)
-40
-50
-60
-70
-40
-50
-60
-70
-80
-80
-90
-90
-100
20
100
1k
10k 20k
-100
20
FREQUENCY (Hz)
100
1k
10k 20k
FREQUENCY (Hz)
Figure 19.
10
100m
OUTPUT POWER (W)
Figure 20.
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Typical Performance Characteristics (continued)
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 3V, RL = 8Ω, input floating
0
0
-10
-10
-20
-20
-30
-30
PSRR LEVEL (dB)
PSRR LEVEL (dB)
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 3V, RL = 8Ω, input 10Ω terminated
-40
-50
-60
-70
-40
-50
-60
-70
-80
-80
-90
-90
-100
20
100
1k
-100
20
10k 20k
100
FREQUENCY (Hz)
1k
10k 20k
FREQUENCY (Hz)
Figure 22.
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 2.6V, RL = 8Ω, input 10Ω terminated
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 2.6V, RL = 8Ω, Input Floating
0
0
-10
-10
-20
-20
-30
-30
PSRR LEVEL (dB)
PSRR LEVEL (dB)
Figure 21.
-40
-50
-60
-70
-40
-50
-60
-70
-80
-80
-90
-90
-100
20
-100
20
100
1k
10k 20k
FREQUENCY (Hz)
100
1k
10k 20k
FREQUENCY (Hz)
Figure 23.
Figure 24.
Open Loop Frequency Response, 5V
Noise Floor, 5V, 8Ω
80kHz Bandwidth, Input to GND
Figure 25.
Figure 26.
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Typical Performance Characteristics (continued)
Power Dissipation vs Output Power, VDD = 5V
1.4
Power Dissipation vs Output Power, VDD = 3V
0.5
0.45
:
POWER DISSIPATION (W)
POWER DISSIPATION (W)
1.2
:
1
0.8
0.6
:
0.4
0.4
0.35
:
0.3
0.25
0.2
0.15
0.1
0.05
0.2
0
0
0
0
0.5
1
1.5
2
2.5
0.2
0.4
0.6
0.8
1
OUTPUT POWER (W)
OUTPUT POWER (W)
Figure 27.
Figure 28.
Power Dissipation vs Output Power, VDD = 2.6V
Shutdown Hysteresis Voltage
VDD = 5V, SD Mode = VDD
0.4
POWER DISSIPATION (W)
0.35
:
0.3
0.25
0.2
:
0.15
0.1
0.05
0
0
12
0.1
0.2
0.4
0.5
0.3
OUTPUT POWER (W)
0.6
Figure 29.
Figure 30.
Shutdown Hysteresis Voltage
VDD = 5V, SD Mode = GND
Shutdown Hysteresis Voltage
VDD = 3V, SD Mode = VDD
Figure 31.
Figure 32.
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Typical Performance Characteristics (continued)
Shutdown Hysteresis Voltage
VDD = 3V, SD Mode = GND
Shutdown Hysteresis Voltage
VDD = 2.6V, SD Mode = VDD
Figure 33.
Figure 34.
Shutdown Hysteresis Voltage
VDD = 2.6V, SD Mode = GND
Output Power vs Supply Voltage, RL = 4Ω
3.5
f = 1kHz
OUTPUT POWER (W)
3
2.5
10% THD+N
2
1.5
1% THD+N
1
500m
0
2.2
3
4
5
5.5
SUPPLY VOLTAGE (V)
Figure 35.
Figure 36.
Output Power vs Supply Voltage, RL = 8Ω
Output Power vs Supply Voltage, RL = 16Ω
3
1000
f = 1kHz
900
OUTPUT POWER (mW)
OUTPUT POWER (W)
2.5
2
10% THD+N
1.5
1
1% THD+N
500m
f=1kHz
800
700
10% THD+N
600
500
1% THD+N
400
300
200
100
0
2.2
3
4
5
5.5
0
2.2
3
4
5
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
Figure 37.
Figure 38.
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Typical Performance Characteristics (continued)
Output Power vs Supply Voltage, RL = 32Ω
Frequency Response vs
Input Capacitor Size
1000
OUTPUT POWER (mW)
900
f=1kHz
800
700
600
500
10% THD+N
400
300
1% THD+N
200
100
0
2.2
3
4
5
5.5
SUPPLY VOLTAGE (V)
Figure 39.
14
Figure 40.
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APPLICATION INFORMATION
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 5, the LM4990 has two internal operational amplifiers. The first amplifier's gain is externally
configurable, while the second amplifier is internally fixed in a unity-gain, inverting configuration. The closed-loop
gain of the first amplifier is set by selecting the ratio of Rf to Ri while the second amplifier's gain is fixed by the
two internal 20kΩ resistors. Figure 5 shows that the output of amplifier one serves as the input to amplifier two
which results in both amplifiers producing signals identical in magnitude, but out of phase by 180°. Consequently,
the differential gain for the IC is
AVD= 2 *(Rf/Ri)
(1)
By driving the load differentially through outputs Vo1 and Vo2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is different from the classical single-ended amplifier
configuration where one side of the load is connected to ground.
A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides
differential drive to the load, thus doubling output swing for a specified supply voltage. Four times the output
power is possible as compared to a single-ended amplifier under the same conditions. This increase in attainable
output power assumes that the amplifier is not current limited or clipped. In order to choose an amplifier's closedloop gain without causing excessive clipping, please refer to the AUDIO POWER AMPLIFIER DESIGN section.
A bridge configuration, such as the one used in LM4990, also creates a second advantage over single-ended
amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across
the load. This eliminates the need for an output coupling capacitor which is required in a single supply, singleended amplifier configuration. Without an output coupling capacitor, the half-supply bias across the load would
result in both increased internal IC power dissipation and also possible loudspeaker damage.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an
increase in internal power dissipation. Since the LM4990 has two operational amplifiers in one package, the
maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power dissipation
for a given application can be derived from the power dissipation graphs or from Equation 2.
PDMAX = 4*(VDD)2/(2π2RL)
(2)
It is critical that the maximum junction temperature TJMAX of 150°C is not exceeded. TJMAX can be determined
from the power derating curves by using PDMAX and the PC board foil area. By adding copper foil, the thermal
resistance of the application can be reduced from the free air value of θJA, resulting in higher PDMAX values
without thermal shutdown protection circuitry being activated. Additional copper foil can be added to any of the
leads connected to the LM4990. It is especially effective when connected to VDD, GND, and the output pins.
Refer to the application information on the LM4990 reference design board for an example of good heat sinking.
If TJMAX still exceeds 150°C, then additional changes must be made. These changes can include reduced supply
voltage, higher load impedance, or reduced ambient temperature. Internal power dissipation is a function of
output power. Refer to the Typical Performance Characteristics curves for power dissipation information for
different output powers and output loading.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. The capacitor location on both the bypass and power supply pins should be as close to the device as
possible. Typical applications employ a 5V regulator with 10µF tantalum or electrolytic capacitor and a ceramic
bypass capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of
the LM4990. The selection of a bypass capacitor, especially CB, is dependent upon PSRR requirements, click
and pop performance (as explained in the section, PROPER SELECTION OF EXTERNAL COMPONENTS),
system cost, and size constraints.
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SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the LM4990 contains shutdown circuitry that is used to
turn off the amplifier's bias circuitry. In addition, the LM4990 contains a Shutdown Mode pin (NGZ and DGQ
packages only), allowing the designer to designate whether the part will be driven into shutdown with a high level
logic signal or a low level logic signal. This allows the designer maximum flexibility in device use, as the
Shutdown Mode pin may simply be tied permanently to either VDD or GND to set the LM4990 as either a
"shutdown-high" device or a "shutdown-low" device, respectively. The device may then be placed into shutdown
mode by toggling the Shutdown pin to the same state as the Shutdown Mode pin. For simplicity's sake, this is
called "shutdown same", as the LM4990 enters shutdown mode whenever the two pins are in the same logic
state. The DGK package lacks this Shutdown Mode feature, and is permanently fixed as a ‘shutdown-low’
device. The trigger point for either shutdown high or shutdown low is shown as a typical value in the Supply
Current vs Shutdown Voltage graphs in the Typical Performance Characteristics section. It is best to switch
between ground and supply for maximum performance. While the device may be disabled with shutdown
voltages in between ground and supply, the idle current may be greater than the typical value of 0.1µA. In either
case, the shutdown pin should be tied to a definite voltage to avoid unwanted state changes.
In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry, which
provides a quick, smooth transition to shutdown. Another solution is to use a single-throw switch in conjunction
with an external pull-up resistor (or pull-down, depending on shutdown high or low application). This scheme
ensures that the shutdown pin will not float, thus preventing unwanted state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers is critical to optimize
device and system performance. While the LM4990 is tolerant of external component combinations,
consideration to component values must be used to maximize overall system quality.
The LM4990 is unity-gain stable which gives the designer maximum system flexibility. The LM4990 should be
used in low gain configurations to minimize THD+N+N values, and maximize the signal to noise ratio. Low gain
configurations require large input signals to obtain a given output power. Input signals equal to or greater than
1Vrms are available from sources such as audio codecs. Please refer to the section, AUDIO POWER
AMPLIFIER DESIGN, for a more complete explanation of proper gain selection.
Besides gain, one of the major considerations is the closed-loop bandwidth of the amplifier. To a large extent, the
bandwidth is dictated by the choice of external components shown in Figure 5. The input coupling capacitor, Ci,
forms a first order high pass filter which limits low frequency response. This value should be chosen based on
needed frequency response for a few distinct reasons.
Selection of Input Capacitor Size
Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized
capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers
used in portable systems, whether internal or external, have little ability to reproduce signals below 100Hz to
150Hz. Thus, using a large input capacitor may not increase actual system performance.
In addition to system cost and size, click and pop performance is effected by the size of the input coupling
capacitor, Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally
1/2 VDD). This charge comes from the output via the feedback and is apt to create pops upon device enable.
Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be
minimized.
Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value.
Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the
LM4990 turns on. The slower the LM4990's outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the
smaller the turn-on pop. Choosing CB equal to 1.0µF along with a small value of Ci (in the range of 0.1µF to
0.39µF), should produce a virtually clickless and popless shutdown function. While the device will function
properly, (no oscillations or motorboating), with CB equal to 0.1µF, the device will be much more susceptible to
turn-on clicks and pops. Thus, a value of CB equal to 1.0µF is recommended in all but the most cost sensitive
designs.
16
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AUDIO POWER AMPLIFIER DESIGN
A 1W/8Ω Audio Amplifier
Power Output
1Wrms
Load Impedance
Given:
8Ω
Input Level
1Vrms
Input Impedance
Bandwidth
20kΩ
100Hz–20kHz ± 0.25dB
A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating
from the Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply
rail can be easily found.
5V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates
headroom that allows the LM4990 to reproduce peaks in excess of 1W without producing audible distortion. At
this time, the designer must make sure that the power supply choice along with the output impedance does not
violate the conditions explained in the POWER DISSIPATION section.
Once the power dissipation equations have been addressed, the required differential gain can be determined
from Equation 3.
(3)
(4)
Rf/Ri = AVD/2
From Equation 3, the minimum AVD is 2.83; use AVD = 3.
Since the desired input impedance was 20kΩ, and with a AVD impedance of 2, a ratio of 1.5:1 of Rf to Ri results
in an allocation of Ri = 20kΩ and Rf = 30kΩ. The final design step is to address the bandwidth requirements
which must be stated as a pair of −3dB frequency points. Five times away from a −3dB point is 0.17dB down
from passband response which is better than the required ±0.25dB specified.
fL = 100Hz/5 = 20Hz
fH = 20kHz * 5 = 100kHz
As stated in the External Components Description section, Ri in conjunction with Ci create a highpass filter.
Ci ≥ 1/(2π*20kΩ*20Hz) = 0.397µF; use 0.39µF
(5)
The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain,
AVD. With a AVD = 3 and fH = 100kHz, the resulting GBWP = 300kHz which is much smaller than the LM4990
GBWP of 2.5MHz. This figure displays that if a designer has a need to design an amplifier with a higher
differential gain, the LM4990 can still be used without running into bandwidth limitations.
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Figure 41. HIGHER GAIN AUDIO AMPLIFIER
The LM4990 is unity-gain stable and requires no external components besides gain-setting resistors, an input
coupling capacitor, and proper supply bypassing in the typical application. However, if a closed-loop differential
gain of greater than 10 is required, a feedback capacitor (C4) may be needed as shown in Figure 2 to bandwidth
limit the amplifier. This feedback capacitor creates a low pass filter that eliminates possible high frequency
oscillations. Care should be taken when calculating the -3dB frequency in that an incorrect combination of R3 and
C4 will cause rolloff before 20kHz. A typical combination of feedback resistor and capacitor that will not produce
audio band high frequency rolloff is R3 = 20kΩ and C4 = 25pf. These components result in a -3dB point of
approximately 320kHz.
18
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Figure 42. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4990
Figure 43. REFERENCE DESIGN BOARD SCHEMATIC
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REVISION HISTORY
Changes from Revision D (May 2013) to Revision E
•
20
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 19
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM4990ITL/NOPB
ACTIVE
DSBGA
YZR
9
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
G
D2
LM4990ITLX/NOPB
ACTIVE
DSBGA
YZR
9
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-40 to 85
G
D2
LM4990MH/NOPB
ACTIVE
HVSSOP
DGQ
10
1000
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 85
4990
LM4990MM/NOPB
ACTIVE
VSSOP
DGK
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
GA5
LM4990MMX/NOPB
ACTIVE
VSSOP
DGK
8
3500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
GA5
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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